In a vehicle roof that is known from German Offenlegungsschrift 35 22 781, a front cover part can be pivoted into a ventilation position about pivot points that are connected with the roof and lying a short distance behind the front edge of the front cover part. In the ventilation position, the rear edge of the front cover part is pushed upward relative to the stationary roof skin and to the rear cover part to form a ventilation gap lying above the roof surface between the rear edge of the front cover part and the front edge of the rear cover part. When the front cover part is pivoted upward into the ventilation position, the aerodynamic properties of the vehicle are negatively influenced, especially at high speeds.
Aerodynamically still more unfavorable are so-called spoiler roofs. One such device is described in German Offenlegungsschrift No. 33 11 452 which discloses a one-piece cover that, after being pivoted out into a ventilation position, can be pushed rearward above the stationary roof membrane.
Another type of ventilation roof, as described in U.S. Pat. No. 4,911,497 includes a roof opening made in a stationary roof skin which can be closed by a one-piece cover that is in active connection on both sides with a control mechanism comprised of front and rear height adjusting mechanisms. The one-piece cover can be pivoted from the closed position into a ventilation position by the front height adjusting mechanisms about a pivoting axis lying at or near the cover's rear edge. In this position, the cover's front edge lies under the plane formed by the roof skin, while the cover's rear edge is kept at least approximately at the height of the stationary roof skin. The cover can then be lowered into an open position by first using the rear height adjusting mechanisms so that its rear edge lies under the stationary roof skin. The lowered cover is then slid rearward under, and approximately parallel to, the stationary roof skin by a drive unit along longitudinal guide mechanisms integral with the roof into the open position in which the cover at least partially opens the roof opening. Such a roof design permits effective ventilation without impairing the aerodynamic properties of the vehicle, even at high speeds. However, in the case of low-lying vehicles, the cover's ventilation position can sometimes result in inadequate headroom.
Also known (U.S. Pat. No. 4,911,496) is a ventilation roof with a two-part cover in which the rear cover part is lowered at its front edge to create a ventilation gap between the rear end of the front cover part and the front edge of the rear cover part.